When a commercial HVAC system relies on glycol to prevent freezing, a reliable method is needed to maintain system pressure. That’s where Armstrong’s GLA Units come in. These automatic fill units are designed to maintain proper pressure in glycol-based systems while preventing contamination, overflow, or system failure.
At Maddock, we stock Armstrong GLA units—ready to ship nationwide—so contractors and engineers can stay on schedule without waiting on long factory lead times. And for systems that don’t use glycol? We go a step further with modified versions that suit a broader range of applications.
What Is a GLA Make-Up Unit?
The GLA (Glycol Auto-Fill) Unit from Armstrong is a pressurized tank and pump system that automatically adds a pre-mixed glycol solution into a closed-loop HVAC system when the system pressure drops. These units are essential in systems exposed to freezing conditions, such as rooftop equipment or buildings that draw in large volumes of cold outdoor air.
The GLA is available in standard and ultra versions, and includes features like low-level shutoff, pump redundancy, alarms, and overflow protection—ideal for facilities where system failure isn’t an option.
Not Using Glycol? We’ve Got You Covered.
While the Armstrong GLA is designed for glycol systems, not all buildings require glycol. In fact, for systems without freeze risk, glycol isn’t always desirable because it can reduce heat transfer efficiency and complicate maintenance.
For those projects, Maddock offers modified versions of these make-up units. Instead of a glycol mix, these systems are designed to refill with plain water, automatically maintaining pressure without compromising your water chemistry or triggering code compliance issues.
Why Not Use City Water to Refill a Glycol Tank?
Here’s where it gets tricky: if a system is running a 30% glycol mix and you introduce untreated city water into the tank, the concentration gets diluted quickly. That disrupts your freeze protection and could lead to hazardous system failures in cold conditions.
That’s why auto-fill functionality is best suited for non-glycol systems unless a secondary glycol mix source is used. Maddock understands this nuance and can help you select the ideal configuration for your job.
Custom Fill Systems That OEMs Won’t Build
Need an automatic water fill system without glycol? Maddock’s team can modify these tanks to help prevent shutdowns caused by an empty reservoir. Over the years, we’ve delivered a range of custom configurations, such as replacing manual fills with float-controlled municipal water connections that automatically maintain tank levels, or adapting units to comply with city code requirements in places like Chicago and New York.
When building codes require a zero-backflow solution, these modified systems can help meet the requirements and keep your project moving forward.
In Stock, Ready to Modify & Available Nationwide
Whether you’re working with glycol or plain water, Maddock can help you get the right make-up unit for your project. We maintain a stock of Armstrong GLA units and can ship them nationwide. Better yet, we’ll help you modify or spec a system that matches your building’s requirements.
Ready to get started or request a custom configuration? Contact us today or shop online to get started.
